1. Field of the Invention
The present invention relates to an ink composition which can yield printed images having high quality on recording media, and an ink jet recording method using the same.
2. Background Art
Ink jet recording is a recording method wherein droplets of ink are ejected through fine nozzles to form letters or figures on the surface of recording media. Various properties are required of inks used in such ink jet recording, and examples thereof include good dispersion stability, ejection stability, and rubbing/scratch resistance of prints.
Inks comprising various water-soluble dyes dissolved in aqueous media have generally been used. Further, inks comprising pigments dispersed in aqueous media have also been provided. Inks comprising pigments dispersed in aqueous media are advantageously superior to inks using water-soluble dyes in waterfastness and lightfastness of printed images.
On the other hand, the use of a pigment in a water-based ink composition poses a problem of dispersion stability. In this case, in order to stably disperse the pigment in an aqueous medium, polymeric dispersants, surfactants or the like are generally used as a dispersant. An ink using a pigment, the surface of which has been subjected to some treatment for enhancing ejection stability, dispersion stability, print density, color development, etc., has also been proposed in the art. For example, Japanese Patent Laid-Open No. 319444/1996 proposes surface-oxidized pigment particles, Japanese Patent Publication No. 94634/1995 and Japanese Patent Laid-Open No. 59715/1996 propose encapsulated fine particles of pigment, and Japanese Patent Laid-Open Nos. 339516/1993, 302227/1996, 302228/1996, and 81647/1996 propose pigment particles with a polymer grafted on the surface thereof.
In addition to the above proposals, proposals on techniques for improving the fixation of pigment on recording media have been made. For example, Japanese Patent Laid-Open No. 218015/1996 proposes an ink using a pigment which has been coated with a resin having a film-forming property at room temperature by a phase inversion emulsion method. Japanese Patent Laid-Open No. 31360/1997 proposes an ink using a pigment which has been coated with an anionic group-containing organic polymer compound by a salting-out method. Japanese Patent Laid-Open No. 286939/1997 proposes an ink using a polymer emulsion wherein fine particles of a polymer have been impregnated with a colorant by a phase inversion emulsion method.
Further, the addition of a resin to an ink composition has been proposed from the viewpoint of improving the fixation of a colorant onto recording media. It is considered that this resin serves as a binder to strongly fix the colorant onto recording media. Regarding resin-containing ink compositions, for example, Japanese Patent Publication No. 1426/1987 proposes an ink comprising a pigment and a resin emulsion dispersed in water, Japanese Patent Laid-Open No. 157668/1980 proposes that a pigment is dispersed in a water-insoluble resin emulsion dispersion, Japanese Patent Laid-Open No. 217088/1989 proposes the use of an emulsion having a specific film-forming temperature, and, likewise, Japanese Patent Laid-Open Nos. 60068/1991 and 18462/1992 propose an ink using a resin emulsion.
Further, the addition of a penetrating agent has been proposed from the viewpoint of improving the penetration of ink into paper. For example, Japanese Patent Laid-Open No. 147861/1981 proposes the use of triethylene glycol monomethyl ether, Japanese Patent Laid-Open No. 111165/1997 proposes the use of ethers of ethylene glycol, diethylene glycol, or triethylene glycol. Further, U.S. Pat. No. 5,156,675 proposes the addition of diethylene glycol monobutyl ether, U.S. Pat. No. 5,183,502 proposes the addition of Surfynol 465, which is an acetylene glycol surfactant manufactured by Nissin Chemical Industry Co., Ltd., and U.S. Pat. No. 5,196,056 proposes the use of diethylene glycol monobutyl ether in combination with Surfynol 465. Furthermore, U.S. Pat. No. 2,083,372 proposes the use of ethers of diethylene glycol in inks.
The present inventors have now found that the use of a water-based pigment dispersion produced by enmicrocapsulation of a pigment in a polymer produced from a polymerizable surfactant having both nonionic hydrophilicity and anionic hydrophilicity and a monomer having a ligand structure, which can combine with a metal ion to form a chelate, can provide an excellent ink composition. In particular, the present inventors have found that the use of the above water-based pigment dispersion can provide an ink composition which, by virtue of excellent dispersion stability and ejection stability, is free from nozzle clogging, can realize stable printing and excellent print quality. The present inventors have further found that a combination of the pigment dispersion with fine particles of a polymer can provide an ink composition which can yield printed images having excellent rubbing/scratching resistance. The present inventors have further found that the deposition of two liquids, that is, the ink composition according to the present invention and a reaction solution containing a reactant capable of producing coagulate upon contact with this ink composition, onto a recording medium to perform printing can realize an ink jet recording method which can improve coagulation and fast drying properties and can provide significantly good print quality. The present invention has been made based on such finding.
Accordingly, it is an object of the present invention to provide an ink composition for ink jet recording, which possesses excellent dispersion stability and ejection stability and can yield printed images having excellent rubbing/scratching resistance, fast drying properties, and print quality, and an ink jet recording method using the same.
According to one aspect of the present invention, there is provided an ink composition for ink jet recording.
The ink composition for ink jet recording according to the present invention comprises at least a water-based pigment dispersion, a water-soluble organic solvent, and water,
the water-based pigment dispersion being such that a pigment has been encapsulated in a polymer produced from a polymerizable surfactant having both nonionic hydrophilicity and anionic hydrophilicity and a monomer having a ligand structure which can combine with a metal ion to form a chelate.
According to another aspect of the present invention, there is provided an ink jet recording method using two liquids.
The ink jet recording method using two liquids according to the present invention comprises the step of depositing, on a recording medium, an ink composition and a reaction solution containing a reactant which, when brought into contact with the ink composition, produces coagulate, thereby performing printing,
the ink composition comprising at least a water-based pigment dispersion, a water-soluble organic solvent, and water,
the water-based pigment dispersion being such that a pigment has been encapsulated in a polymer produced from a polymerizable surfactant having both nonionic hydrophilicity and anionic hydrophilicity and a monomer having a ligand structure which can combine with a metal ion to form a chelate.